104 CONTRIBUTIONS TO CANADIAN PALEONTOLOGY. 



besides the septa, are rather distant, thin and laminar horizontal 

 diaphragms, which partake partly of the nature of tabulae and partly 

 of dissepiments. These diaphragms either form almost continuous 

 floors across the corallites (at intervals of from one to two millimetres 

 apart) and thus resemble tabulae, except that their continuity appears to 

 be interrupted by the septa, or they are disconnected and not on the same 

 plane and thus partake more of the nature of dissepiments, though they 

 are never curved." (Whiteaves.) 



Of this species Dr. Whiteaves says : " It is clearly congeneric, and 

 may even prove to be conspecific, with the Cyathophylloides Rhenanum 

 of Freeh, from the Devonian rocks of the Eifel, which Dr. Freeh informs 

 the present writer (Dr. Whiteaves) is also a Columnar ia." 



This coral, as its name implies, has corallites which are normally separ- 

 ate and cylindrical, but when at times they are crowded together they 

 become polygonal, as is shown by some of the specimens in the col- 

 lection. 



C. disjuncta may be regarded as an extreme form of the genus ; C. 

 alveolata and C. Haiti are species in which the corallites are contiguous, 

 C. rugosa and C. calicina species in which the corallites are as often 

 free as in contact and C. disjuncta, a species in which the corallites are 

 generally free. 



Devonian (American Stringocephalus zone*). Pentamerus Point, Lake 

 Manitoba, J. B. Tyrrell and J. F. Whiteaves, 1888. South-west shore of 

 Dawson Bay, Lake Winnipegosis, at the mouth of Steep Rock River, J. 

 B. Tyrrell, 1889. 



4. Madreporaria Rugosa. 

 CYATHAXONTDAE. 



Genus Petraia, Miinster, 1839. 



Petraia, Miinster. 1839. Beitr. zur. Petrefaktenkunde, vol. I., p. 42. 



Corallum simple, conical, small. Epitheca complete. Calyx deep at 

 times reaching almost to base of corallum. Septa of two orders, prim- 

 aries and secondaries, little developed. Sometimes a cardinal and two 

 alar septa are conspicuous. The tetrameral arrangement of the septa 

 well indicated by the septal furrows on the surface. Septal fossette 

 sometimes present. No tabulae dissepiments nor columella. 



Type species. — P. decussata, Miinster. 



Range. — In Canada, Cambro-Silurian, Silurian. 



*The term "American Stringocephalus zone " is used at Dr. Whiteaves 's suggestion, 

 until we know whether it is synchronous with the European " Stringocephalus zone " or 

 not. 



